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Nothomyrmecia
Nothomyrmecia, also known as the dinosaur ant or dawn ant, is a rare genus of ants consisting of a single species, Nothomyrmecia macrops. These ants live in South Australia, nesting in old-growth mallee woodland and Eucalyptus woodland. The full distribution of Nothomyrmecia has never been assessed, and it is unknown how widespread the species truly is; its potential range may be wider if it does favour old-growth mallee woodland. Possible threats to its survival include habitat destruction and climate change. Nothomyrmecia is most active when it is cold because workers encounter fewer competitors and predators such as Camponotus and Iridomyrmex, and it also increases hunting success. Thus, the increase of temperature may prevent them from foraging and very few areas would be suitable for the ant to live in. As a result, the IUCN lists the ant as Critically Endangered. As a medium-sized ant, Nothomyrmecia measures 9.7–11 mm (0.38–0.43 in). Workers are monomorphic, showing little morphological differentiation among one another. Mature colonies are very small, with only 50 to 100 individuals in each nest. Workers are strictly nocturnal and are solitary foragers, collecting arthropod prey and sweet substances such as honeydew from scale insects and other Hemiptera. They rely on their vision to navigate and there is no evidence to suggest that the species use chemicals to communicate when foraging, but they do use chemical alarm signals. A queen ant will mate with one or more males and, during colony foundation, she will hunt for food until the brood have fully developed. Queens are univoltine (they produce just one generation of ants each year). Two queens may establish a colony together, but only one will remain once the first generation of workers has been reared. Nothomyrmecia was first described by Australian entomologist John S. Clark in 1934 from two specimens of worker ants. These were reportedly collected in 1931 near the Russell Range, inland from Israelite Bay in Western Australia. After its initial discovery, the ant was not seen again for four decades until a group of entomologists rediscovered it in 1977, 1,300 km (810 mi) away from the original reported site. Dubbed as the 'Holy Grail' of myrmecology, the ant was subject to great scientific interest after its rediscovery, attracting scientists from around the world.23 In Poochera (the rediscovery site), pictures of the ant are stencilled on the streets, and it is perhaps the only town in the world that thrives off ant-based tourism. Some entomologists have suggested a relationship to the Baltic Eocene fossil ant genus Prionomyrmex based on morphological similarities, but this interpretation is not widely accepted by the entomological community. Owing to its body structure, Nothomyrmecia is regarded to be the most plesiomorphic ant alive and a 'living fossil', stimulating studies on its morphology, behaviour, ecology, and chromosomes. Description Nothomyrmecia is a medium-sized ant measuring 9.7–11 mm (0.38–0.43 in) in length. Workers are monomorphic, meaning that there is little morphological differentiation among one another.245 The mandibles, clypeus (one of the sclerites that make up the "face" of an arthropod or insect), antennae and legs are pale yellow. The hairs on the body are yellow, erect and long and abundant, but on the antennae and legs they are shorter and suberect (standing almost in an erect position). It shows similar characteristics to Myrmecia, and somewhat resembles Oecophylla, commonly known as weaver ants. Workers are strictly nocturnal (active mainly at night) but navigate by vision, relying on large compound eyes.46 The mandibles are shorter than the head. They have 10 to 15 intermeshing teeth and are less specialized than those of Myrmecia and Prionomyrmex, being elongate and triangular. The head is longer than it is wide and broader towards the back. The sides of the head are convex around the eyes. The long antennal scapes (the base of the antenna) extend beyond the occipital border, and the second segment of the funiculus (a series of segments between the base and club) is slightly longer than the first, third and fourth segment. The node, pronotum, epinotum and thorax are longer than broad, and the mesonotum is just as long as it is wide. The first segment of the gaster (the bulbous posterior portion of the metasoma) is broader than long by a third and broader at the back than the front with strongly convex sides.47 A long and retractable stinger is present at the rear of the abdomen. It has been described as "prominent and effective" and is capable of inflicting a painful sting to humans.24 A 'sting bulb gland' is also present in Nothomyrmecia; this is a small exocrine gland of unknown function, first discovered and named in 1990. It is situated in the basal part of the insect's sting, and is located between the two ducts of the venom gland and the Dufour's gland.8 Despite its many plesiomorphic features, the sting apparatus of Nothomyrmecia is considered less primitive than those found in other ants such as Stigmatomma pallipes.9 It is the only known species of ant that contains both a sting and a 'waist' (i.e. it has no postpetiole between the first and second gastral segments). Queens look similar to workers, but several morphological features distinguish the two castes from each other. The queen's body is usually larger. Ocelli are highly developed, but the eyes on the queen are not enlarged. The structure of the pterothorax (the wing-bearing area of the thorax) is consistent with other reproductive ants, but it does not occupy as much of its mesosomal bulk. The wings of the queens are reduced to the point that they are not functional (they are brachypterous).211 Their wings are rudimentary and stubby, barely overlapping the first gastral segment. Males resemble those of Myrmecia, but Nothomyrmecia males bear a single waist node. The wings on the male ant are not stubby like a queen's; rather they are long and fully developed, exhibiting a primitive venational complement. They have a jugal anal lobe (a portion of the hindwing), a feature found in many primitive ants, and basal hamuli (hook-like projections that link the forewings and hindwings). Most male specimens collected have two tibial spurs (spines located on the distal end of the tibia); the first spur is a long calcar and the second spur is short and thick. Adults have a stridulatory organ on the ventral side of the abdomen – unlike all other hymenopterans in which such organs are located dorsally.2 In all castes, these ants have six maxillary palps (palps that serve as organs of touch and taste in feeding) and four labial palps (sensory structures on the labium), a highly primitive feature. The females have a 12-segmented antenna, whereas males have 13 segments. Other features include paired calcariae found on both the hind and middle tibiae, and the claws have a median tooth. The unspecialized nature of the cuticle (outer exoskeleton of the body) is similar to Pseudomyrmex, a member of the subfamily Pseudomyrmecinae. Many of the features known in Nothomyrmecia are found in Ponerinae and Pseudomyrmecinae. The eggs of Nothomyrmecia are similar to those of Myrmecia, being subspherical and non-adhesive. The larvae bear a primitive body structure with no specialized tubercles, sharing similar characteristics with the subfamily Ponerinae, but the sensilla are more abundant on the mouthparts. The larvae are characterized into three stages: very young, young, and mature, measuring 2.8 mm (0.1 in), 6.3 mm (0.2 in) and 11 mm (0.4 in), respectively.12 The cocoons have thin walls and produce meconium (a metabolic waste product expelled through the anal opening after an insect emerges from its pupal stage).2 The cuticular hydrocarbons have internally branched alkenes, a feature rarely found in ants and most insects.13 In general, the body structure of all Nothomyrmecia castes demonstrates the primitive nature of the species.2 Notable derived features include vestigial ocelli on workers, brachypterous queens, and the mesoscutal structure on males. The morphology of the abdomen, mandibles, gonoforceps (a sclerite, serving as the base of the ovipositors sheath) and basal hamuli show it is more primitive than Myrmecia. The structure of the abdominal region can separate it from other Myrmeciinae relatives (the fourth abdominal segment of Myrmecia is tubulate, whereas Nothomyrmecia has a non-tubulated abdominal segment). The appearance of the fourth abdominal segment is consistent with almost all aculeate insects, and possibly Sphecomyrma.2 The feature of non-functional, vestigial wings may have evolved in this species relatively recently, as wings might otherwise have long-since disappeared completely had they no function for dispersal. Wing-reduction could somehow relate to population structure or some other specialized ecological pressure. Equally, wing-reduction might be a feature that only forms in drought-stressed colonies, as has been observed in several Monomorium ant species found throughout semi-arid regions of Australia. As yet, scientists do not fully understand how the feature of non-functional, vestigial wings arose in Nothomyrmecia macrops. Taxonomy Discovery The first collection of Nothomyrmecia was made in December 1931 by amateur entomologist, Amy Crocker,a whose colleagues had collected a range of insect samples for her during a field excursion, including specimens of two worker ants, reportedly near the Russell Range, inland from Israelite Bay in Western Australia.24 Crocker then passed the ants to Australian entomologist John S. Clark. Recognized shortly afterwards as a new species, these specimens became the syntypes.4 Entomologist Robert W. Taylor subsequently expressed doubt about the accuracy of recording of the original discovery site, stating the specimens were probably collected from the western end of the Great Australian Bight, south from Balladonia.2 The discovery of Nothomyrmecia and the appearance of its unique body structure led scientists in 1951 to initiate a series of searches to find the ant in Western Australia.6 Over three decades, teams of Australian and American collectors failed to re-find it; entomologists such as E. O. Wilson and William Brown, Jr., made attempts to search for it, but neither was successful.14 Then, on 22 October 1977, Taylor and his party of entomologists from Canberra serendipitously discovered a solitary worker ant at Poochera, South Australia, southeast of Ceduna, some 1,300 km (810 mi) from the reported site of the 1931 discovery.215 In 2012, a report discussing the possible presence of Nothomyrmecia in Western Australia did not confirm any sighting of the ant between Balladonia and the Western Australian coastal regions.16 After 46 years of searching for it, entomologists have dubbed the ant the 'Holy Grail' of myrmecology. Naming In 1934 entomologist John S. Clark published a formal description of Nothomyrmecia macrops as a new species and within a completely new genus and tribe (Nothomyrmecii) of the Ponerinae.4 He did so because the two specimens (which then became the syntypes) bore no resemblance to any ant species he knew of, but they did share similar morphological characteristics with the extinct genus Prionomyrmex. Clark notes that the head and mandibles of Nothomyrmecia and Prionomyrmex are somewhat similar, but the two can be distinguished by the appearance of the node (a segment between the mesosoma and gaster).4 In 1951, Clark proposed the new ant subfamily Nothomyrmeciinae for his Nothomyrmecia, based on morphological differences with other ponerine ants.19 This proposal was rejected by American entomologist William Brown Jr., who placed it in the subfamily Myrmeciinae with Myrmecia and Prionomyrmex, under the tribe Nothomyrmeciini.20 Its distant relationship with extant ants was confirmed after its rediscovery, and its placement within the Formicidae was accepted by most scientists until the late 1980s.221 The single waist node led scientists to believe that Nothomyrmecia should be separate from Myrmecia and retained Clark's original proposal. This proposal would place the ant into its own subfamily, despite many familiar morphological characteristics between the two genera. This separation from Myrmecia was retained until 2000. In 2000, entomologist Cesare Baroni Urbani described a new Baltic fossil Prionomyrmex species (P. janzeni). After examining specimens of Nothomyrmecia, Baroni Urbani stated that his new species and N. macrops were so morphologically similar that they belonged to the same genus. He proposed that the name Prionomyrmex should replace the name Nothomyrmecia (which would then be just a synonym), and also that the subfamily Nothomyrmeciinae should be called Prionomyrmeciinae.24 In 2003, Russian palaeoentomologists G. M. Dlussky and E. B. Perfilieva separated Nothomyrmecia from Prionomyrmex on the basis of the fusion of an abdominal segment.25 In the same year, American entomologists P. S. Ward and S. G. Brady reached the same conclusion as Dlussky and Perfilieva and provided strong support for the monophyly of Prionomyrmex. Ward and Brady also transferred both taxa as distinct genera in the older subfamily Myrmeciinae under the tribe Prionomyrmecini.2526 In 2005 and 2008, Baroni Urbani suggested further evidence in favor of his former interpretation as opposed to Ward and Brady's.2728 This view is not supported in subsequent relevant papers, which continue to use the classification of Ward and Brady, rejecting that of Baroni Urbani.29303132 The ant is commonly known as the dinosaur ant, dawn ant, or living fossil ant because of its plesiomorphic body structure.103033 The generic name Nothomyrmecia means "false bulldog ant".10 Its specific epithet, macrops ("big eyes"), is derived from the Greek words makros, meaning "long", or "large", and ops, meaning "eyes". Genetics and phylogeny Studies show that all hymenopteran insects that have a diploid (2n) chromosome count above 52 are themselves all ants; Nothomyrmecia and another Ponerinae ant, Platythyrea tricuspidata, share the highest number of chromosomes within all the Hymenoptera, having a diploid chromosome number of 92–94.236 Genetic evidence suggests that the age of the most recent common ancestor for Nothomyrmecia and Myrmecia is approximately 74 million years old, giving a likely origin in the Cretaceous.26 There are two hypotheses of the internal phylogeny of Nothomyrmecia: subfamily Formicinae is more closely related to Nothomyrmecia than it is to Myrmecia, evolving from Nothomyrmecia-like ancestors. Alternatively, Nothomyrmecia and Aneuretinae may have shared a common ancestor; the two most likely separated from each other, and the first formicines evolved from the Aneuretinae instead. Currently, scientists agree that Nothomyrmecia most likely evolved from ancestors to the Ponerinae.37 Nothomyrmecia and other primitive ant genera such as Amblyopone and Myrmecia exhibit behavior similar to a clade of soil-dwelling families of vespoid wasps.38 The following cladogram generated by Canadian entomologist S. B. Archibald and his colleagues shows the possible phylogenetic position of Nothomyrmecia among some ants of the subfamily Myrmeciinae. They suggest that Nothomyrmecia may be closely related to extinct Myrmeciinae ants such as Avitomyrmex, Macabeemyrma, Prionomyrmex, and Ypresiomyrma. |2= }} }} }} Distribution and Habitat Category:Ants